Lactose, or milk sugar, is a white crystalline disaccharide. It is formed in the mammary glands of all lactating animals and is present in their milk. Lactose yields D-galactose and D-glucose on hydrolysis by lactase (β-galactosidase), an enzyme found in gastric juice. People who lack this enzyme after childhood cannot digest milk and are said to be lactose intolerant. Common symptoms of lactose intolerance include nausea, cramps, gas and diarrhea, which begin about 30 minutes to 2 hours after eating or drinking foods containing lactose. Between 30 and 50 million Americans are lactose intolerant. Certain ethnic and racial populations are more widely affected than others. As many as 75 percent of all African-Americans and Native Americans and 90 percent of Asian-Americans are lactose intolerant. The condition is least common among persons of northern European descent. There is thus a need in the food and beverage industry to be able to rapidly and accurately measure lactose levels.
Galactos(a)emia, characterised by the deficiency of one or more enzymes required by an infant to metabolise D-galactose, is a serious and potentially life-threatening disease. If undiagnosed, D-galactose rapidly builds-up in the blood of newborn babies, and can cause cataracts, growth and mental retardation, liver damage and even death. The occurrence of Galactos(a)emia is approximately 1 in 20,000, and tests for the condition form part of a panel of assays performed as part of newborn screening programs. There are two types of enzymatic test used for the diagnosis of Galactos(a)emia; the first is designed to identify the deficiency of galactose-1-phosphate uridyltransferase, the predominant cause of the condition, and the second quantifies total blood D-galactose (comprising free D-galactose and that in the form of D-galactose-1-phosphate), thus identifying Galactos(a)emia regardless of the cause. Once diagnosed, a sucrose based milk formula free of lactose ensures healthy development of the child. There is thus an established and appreciated requirement to rapidly and accurately determine D-galactose in the clinical environment.
Arabinose finds applications in the flavour, food and pharmaceutical industries, for example in controlled Maillard reactions, as a sweetener, and when derivatised as an antiviral agent, respectively. As L-arabinose is one of the most abundant pentoses on earth, much research activity is focused on the di-, oligo- and polysaccharides that contain this monosaccharide, such as arabinooligosaccharides, arabinoxylans, arabinogalactans and arabinans. Thus, there is a general requirement for a simple and rapid test for L-arabinose. Similarly, much research is performed on di-, oligo- and polysaccharides containing D-galactose, such as galactosyl-sucrose oligosaccharides (such as raffinose), galactooligosaccharides, galactans, galactomannans, arabinogalactans, and glycoforms of glycoproteins, and thus there is also a requirement for a simple and rapid test for D-galactose in this area.
There is a large and well established market for the enzymatic determination of free D-galactose and D-galactose as released from lactose, especially in milk and dairy products, but also in many other foodstuffs and materials. Enzymatic methods for the measurement of lactose are well known and are generally based on the hydrolysis of lactose to D-glucose and D-galactose with β-galactosidase followed by determination of either D-galactose or D-glucose. Quantification by measurement of the released D-galactose is greatly preferred, as foodstuffs in general contain much higher levels of free D-glucose than free D-galactose. However, due to an inherent rate limiting factor fundamental to the biochemistry employed, all current products are very slow, taking between 20 and 40 minutes to complete, and optimally require incubation at a high temperature of approximately 40° C., as compared to the optimal time expected/preferred by the modern analyst of between 2 and 5 minutes (and at ambient room temperature). The fundamentals of the currently employed methods for the measurement of free D-galactose and D-galactose as released from lactose and earlier citations can be found in Beutler, H.-O. (1988). Lactose and D-Galactose. In Methods of Enzymatic Analysis (Bergmeyer, H. U., ed.), 3rd ed., Vol. VI, pp. 104-112, VCH Publishers (UK) Ltd, Cambridge, UK. Those for the measurement of free L-arabinose can be found in Sturgeon R. J. (1988). L-Arabinose. Also in Methods of Enzymatic Analysis pp. 427-431.
An enzymatic test kit for lactose and D-galactose, based on the existing traditional methodology using just β-galactose dehydrogenase, is currently offered by Megazyme (cat. no. K-LACGA), as well as Boehringer Mannheim GmbH, Roche (via R-biopharm), and Scil Diagnostics GmbH.